In order to create Optional we need to suply 2 functions: set and getOption

Composes Optional a b with Optional b c and returns Optional a c

string2IntPrism : Prism String Int
string2IntPrism = Prism (String.toInt >> Result.toMaybe) toString


addressRegionIntOptional: Optional Address Int
addressRegionIntOptional = addressRegionOptional `compose` (fromPrism string2IntPrism)

Composes Optional a b with Lens b c and returns Optional a c

string2CharListIso : Iso String (List Char)
string2CharListIso = Iso String.toList String.fromList


addressRegionListCharOptional: Optional Address (List Char)
addressRegionListCharOptional = addressRegionOptional `composeLens` (fromIso string2CharListIso)

Modifies given function (b -> b) to be (a -> Maybe a) using Optional a b

    modifyRegion: String -> String
    modifyRegion region = String.reverse region


    modifyAddressRegion: Address -> Maybe Address
    modifyAddressRegion address = Optional.modifyOption addressRegionOptional modifyRegion address

Modifies given function (b -> b) to be (a -> a) using Optional a b

    modifyRegion: String -> String
    modifyRegion region = String.reverse region


    modifyAddressRegion: Address -> Address
    modifyAddressRegion address = Optional.modify addressRegionOptional modifyRegion address

Zip Optional a c with Optional b d to form Optional for the pairs ( a, b ) ( c, d )

Casts Prism a b to Optional a b

string2IntPrism : Prism String Int
string2IntPrism =
    Prism (String.toInt >> Result.toMaybe) toString


stringIntOptional: Optional String Int
stringIntOptional = fromPrism string2IntPrism

Casts Lens a b to Optional a b where getOption will return always Just